Is a Calorie a Calorie?

By Mark Bittman The New York Times

I was looking forward to “Why Calories Count,” the new book by Marion Nestle and Malden Nesheim. I figured gaining an advanced education in calories might allow me to better understand diet and weight gain. These two are not faddists but clear thinkers: actual scientists. But of course there is more to weight gain than the calorie.

This was obvious from the moment I asked Ms. Nestle a key question: “Is a calorie a calorie?” This sounds simple, and if the answer is “yes,” all you do is take in fewer calories than you expend and you’ll lose weight. It need go no further than that.

It might help to first define a calorie, and that’s easy: it’s a measure of the energy derived from a food source. A gram of fat has been determined to have nine calories and a gram of protein or carbohydrate four calories; so for any given measure, fat has more than twice as many calories as protein or carbs. Those numbers are not perfectly accurate, but they’re good enough.